The present invention relates to a diaphragm used with acoustic transducers such as speakers, microphones and the like.
The diaphragm of this type now on the market has been formed of natural fibers by known paper making processes, and enjoyed wide use due to its small mass, relatively large modulus of longitudinal elasticity (a Young's modulus), properly large internal loss, etc. To add to this, the said diaphragm can easily be formed into any complicated shape by the paper making processes.
The diaphragm formed of natural fibers, e.g., wood pulp fibers or strip-like materials, excels in various properties as mentioned above; however, there is now an increasing demand for a new version of diaphragms which are formed of another material capable of producing sounds of different tone quality, adapted to changes in life style and the preference of audio fans. To meet such a demand, the use of thermoplastic or thermosetting resins, e.g., polyvinyl chloride or polyamide, has been proposed. However, the products formed of these resins have the disadvantages that most of them are virtually combustible and, hence, liable to catch fire. With speakers or the like parts, their voice coils may generate heat due to excessive inputs, or may be exposed to high temperatures as is the case with television cabinets. The speakers per se as well as their parts inclusive of diaphragms should thus be made fire retardant.
Inorganic asbestos is a typical example of the flame retardant materials used widely in the art, but is unpreferable in view of tone quality, and is deficient in sensitivity due to its large mass. Furthermore, the asbestos shows a low degree of internal loss, and tends to give rise to high frequency distortion and, hence, fluctuations in the frequency properties, especially in high-pitched sound regions.